It is often necessary to measure the surface characteristics of painted, plated, polished or otherwise finished objects in the course of their manufacture. Among the measurements which are commonly made are gloss, which is a measure of the dispersion with which light is reflected from a surface, distinctness of image, which is a measure of how clearly an object is reflected by a surface as well as orange peel and roughness, which are measurements of surface texture. Orange peel is a surface characteristic which is dependent upon the presence of surface features having a texture in the general size range of 0.05 to 1 millimeter, which produce texture appearing somewhat reminiscent of the skin of an orange. Orange peel is notoriously difficult to quantify with any accuracy because of the size and periodicity of the features.
In the prior art, orange peel measurements are made on a subjective basis by comparing a finished surface with a set of standards. This system of measurement is inaccurate, time consuming and expensive; hence, efforts have been made to automate orange peel measurements. Instrumental approaches to orange peel measurement typically involve the analysis of light reflected from the surface. The features comprising the orange peel texture reflect light at varying angles, and the changing pattern of reflectivity produced as a beam of light is scanned across a surface is analyzed to produce a signal indicative of the degree of orange peel. Analysis typically involves a determination of the rate of change and/or periodicity of the reflected light pattern.
Automated orange peel measuring systems of the prior art suffer from a lack of repeatability in their measurements. It is not unusual for repeat measurements of standard orange peel samples to vary by 30-60% when made with instruments of the prior art. In addition, orange peel measurements are most preferably made on site during the manufacture of items, particularly motor vehicles, household appliances and the like. Therefore, the measuring equipment is utilized in a production environment and typically encounters high levels of vibration, dust and vapors, all of which adversely affect the accuracy of readings made with the prior art equipment.
The production environment also mandates that the measuring equipment be relatively small in size, self-contained and easy to use and it is further desirable that the system be capable of operating for at least one full production shift without recharging or replacement of a power source. It is further desirable that the system be capable of storing data for archival purposes or subsequent analysis.
The system of the present invention provides a small, simple to use, self-contained instrument for measuring orange peel of finished surfaces. The system of the present invention is designed so as to be relatively insensitive to vibration and to be completely enclosed so as to eliminate problems from ambient pollutants. These and other advantages of the present invention will be readily apparent from the drawings, discussion and description which follow.